MRI All-In-One Flashcards

Question

FDA SAR LIMITS | Torso

Answer 1

8 W/kg / 5 min

Answer 2

12 W/kg / 5 min

Answer 3

An increase in the amplitude of the T wave on an ECG due to the strength of the static magnetic field

Answer 4

The process of "seeing stars" when sensory receptors in the retina are stimulated by the changing magnetic field

Answer 5

< 1 month - 4T | > 1 month - 8T

Answer 6

Patients with hypertension, diabetes, or over 60 years of age

Answer 7

Patients with hepatocellular disease

Answer 8

IVC clot filter

Answer 9

Law of electromagnetic induction

Answer 10

For electromagnetic induction to take place, a conductor, magnetic field, and motion (between the two) must be present

Answer 11

An electromagnetically induced current within a conductor creates a magnetic field opposing the magnetic field that produced the electromagnetically induced current (eddy currents)

Answer 12

- Superconductive electromagnet - Resistive electromagnet - Permanent magnet

Answer 13

- Constructed from niobium and titanium - 0.3-8T - Requires no additional power - Most expensive

Answer 14

2 K (below 4K is considered superconductive)

Answer 15

- Current carrying loop of wire - Less than 0.3T - Requires constant power

Answer 16

- Composed of ALNICO - Less than 0.3T - Don't need power or cryogen - Least expensive but worst magnetic field homogeneity

Answer 17

10,000G or 10kG

Answer 18

Low - less than 0.35T Mid - 0.5-0.7T High - 1-1.5T Ultra-high - greater or equal to 3T

Answer 19

- Have paired orbital electrons (no magnetic moment) - Repel external magnetic field slightly - Copper, oxygen, silver, mercury, lead, water, graphite

Answer 20

- Have unpaired orbital electrons (small positive magnetic moment of <1) - Slightly attract external magnetic field and align - Tungsten, cesium, lithium, aluminum, magnesium, sodium, platinum, gadolinium contrast agents

Answer 21

- Intermediate magnetic moment (between paramagnetic and ferromagnetic) - Only display a magnetic moment in bulk, individual molecules have no magnetic moment - Iron oxide particles, iron oxide contrast agents (generally used as T2 or T2* contrast agents in the liver)

Answer 22

- Have half-filled electron shells (large magnetic moment of >1) - Attract external magnetic field with great strength - Retain their magnetization - Steel, iron, nickel, cobalt

Answer 23

- Increase in SNR | - Increase in chemical shift artifacts

Answer 24

- Decrease in SNR | - Decrease in chemical shift artifacts

Answer 25

- Time it takes for a gradient to achieve maximum gradient amplitude - Describes the speed and strength of the gradients - Measured in mT/m/s - Typically 70-200 mT/m/s - Best indicator of overall gradient performance

Answer 26

Dividing the maximum gradient amplitude by the rise time

Answer 27

- Maximum strength or slope that is achievable by a particular gradient - Measured in mT/m or G/cm - Typically 10-40 mT/m (most commonly 33 mT/m in modern systems)

Answer 28

- Time it takes for a gradient to switch on, achieve the required gradient strength/slope, and switch off - Measured in microseconds

Answer 29

- Time that a gradient is capable of working at a maximum amplitude - Usually expressed as % - Nearly 100% can be achieved on modern systems

Answer 30

Mathematical equation that determines the value of the precessional frequency of nuclei in the presence of an external magnetic field

Answer 31

42.57 mHz/T

Answer 32

- Spins flip into the transverse plane | - Spins begin to precess in-phase (become coherent)

Answer 33

Natural decay of the NMV after the RF is turned off

Answer 34

- Aka "spin-lattice relaxation" and "longitudinal relaxation" - Time it takes for 63% of the longitudinal magnetization (Mz) to recover in tissues - For SEPS, controlling factor is TR - For GEPS, controlling factors are TR and flip angle - For IRPS, the controlling factors are TR and TI

Answer 35

Fat - 200 ms | Water - 2500 ms

Answer 36

- Aka "spin-spin relaxation" and "transverse decay" - Time it takes for 63% of transverse magnetization (Mxy) to decay - Controlling factor during all pulse sequences is TE

Answer 37

Fat - 100 ms | Water - 2500 ms

Answer 38

- Aka "susceptibility decay" | - Similar to T2 decay, except that transverse decay occurs quicker due to the combination of T2 decay and T2 prime

Answer 39

The dephasing of precessing spins due to magnetic field inhomogeneities

Answer 40

- Aka "spin density" | - Represents the relative number of mobile hydrogen protons per unit volume

Answer 41

- A vector produced as a result of excess hydrogen nuclei aligning with the main magnetic field - Increases with increasing magnetic field strength, and results in improved signal from the patient

Answer 42

- Slice selection - Phase encoding - Frequency encoding

Answer 43

- Switches on during the application of the alpha pulse and any subsequent RF rephasing pulses applied during a pulse sequence - The scan plan selected during slice prescription determines which of the three physical gradients performs slice selection during the transmission of an RF pulse

Answer 44

- Usually spatially encodes the signal sampled along the short axis of anatomy within a slice - Energizes after the application of the alpha pulse and before the application of the rephasing pulse - Applied slope and polarity of the phase-encoding gradient determines which line of k-space will be filled during readout

Answer 45

- Aka "readout gradient" - Usually spatially encodes the signal sampled along the long axis of anatomy within a slice - Applied during the collection of the echo to allow the system to sample data for storage in k-space

Answer 46

- Spatial frequency domain that serves as a temporary storage space for data collected during image acquisition - Rectangular and has two axes; the phase axis (y-axis), and the frequency axis (x-axis) - Steep phase encoding gradient slope stores spatial resolution info (low signal amplitude) on the outer edges - Shallow phase encoding gradient slope encodes contrast info (high signal amplitude) into the center - Physically located in the array processor

Answer 47

- Mathematical process that converts data obtained during image acquisition so that it may be stored in k-space - Also applied when data is removed from k-space for image formation

Answer 48

- Swapping phase and frequency encoding axes - Placing pre-saturation pulses - Employing motion reduction techniques (increasing NSA, using Propeller sequences, increasing concatenations improving patient comfort, etc.)

Answer 49

- Enlarging the FOV in the phase direction - Placing pre-saturation pulses - Using no phase wrap (phase oversampling, anti-foldover) - Proper centering of the anatomy to the coil - Disengaging coils that are not needed

Answer 50

- Increasing NSA (NEX) | - Increasing phase encoding matrix

Answer 51

- Magnetic field strength (higher) - Receive bandwidth (narrower) - Pixel size (larger)

Answer 52

- Increasing receive bandwidth - Decreasing pixel size (small FOV, large matrix) - Scanning at lower field strengths

Answer 53

- Using SE sequences (since 180 degree RF pulses are efficient at rephasing) - Applying a TW interval of 4.2ms (when fat and water are in phase with each other)

Answer 54

- Using FSE sequence with a long ETL (since multiple 180 degree RF pulses are more efficient at rephasing) - Decreasing the TE (long TE allows more dephasing from inhomogeneities) - Removing metallic objects

Answer 55

-Make sure there is no RF leaks into the scanner room

Answer 56

-Decreasing voxel size by using a small FOV, large matrix, and thin slices

Answer 57

- Careful placement of multiple stacks of slices | - Reducing slice angle when multiple stacks of slices are used

Answer 58

- Using a gap space of at least 30% the slice thickness | - Using interleaving option instead of the sequential option

Answer 59

- Using SE pulse sequences (to compensate for field inhomogeneities) - Keeping patient anatomy away from bore - Making sure that all the anatomy fits in the FOV (to prevent wrap)

Answer 60

- Reducing the acceleration factor (R factor) | - Proper use of a calibration scan

Answer 61

- Altering the angle of the anatomy | - Lengthening the TE applied (since T2 decay is no slower)

Answer 62

1T - 147 Hz 1.5T - 220 Hz 2T - 440 Hz

Answer 63

- Phase Mismapping (phase ghosting, motion artifact, flow artifact) - Aliasing (phase wrap, wrap-around artifact) - Truncation (Gibbs artifact) - Parallel Imaging Artifact

Answer 64

- Chemical Shift (type 1 artifact) | - Radiofrequency Artifact (zipper artifact)

Answer 65

- Chemical Misregistration (type 2 artifact aka out-of-phase artifact) - Magnetic Susceptibility

Answer 66

-Moire Pattern

Answer 67

1. Acceptance testing 2. Establishing baseline performance 3. Detection and diagnosis of changes in equipment performance 4. Correction verification

Answer 68

- Annually using AMAP | - 5.0mm +- 0.7mm with axial T1 ACR series

Answer 69

- Weekly using AMAP - 1.0mm or better with axial T1 ACR series - All four holes in at least one row of the AP image should be recognized as separate and distinct points.

Answer 70

- Weekly using AMAP | - Should be reported if the number of visible spokes is reduced by more than three.

Answer 71

- Weekly using AMAP - To detect off-resonance operation in an attempt to prevent a consequential reduction in SNR - Should not deviate by more than 1.5ppm between weekly measurements

Answer 72

- Weekly using AMAP - To determine problems with the RF chain by acquiring several signals while varying the transmitter attenuation (or gain) so that imaging can proceed using the proper flip angle - Any changes in transmit gain exceeding the prescribed action limited should be reported

Answer 73

- Weekly using AMAP | - Should be +- 2mm of the actual values when using a 25cm FOB

Answer 74

- At least weekly and can include: - Bed transport system - Alignment and system indicator lights - RF room integrity - Emergency cart - Safety lights - Signage - Monitors, coils, cables

Answer 75

- The difference in the SNR between two adjacent pixels | - Has the greatest influence on image quality and is controlled by the same factors as SNR

Answer 76

- The ratio of signal amplitude to the average amplitude of the noise - Most greatly affected by the size of the FOV

Answer 77

- The ability of the imaging system to detect two points as separate and distinguishable - Enhanced by square pixels but the ONLY characteristic that directly affects spatial resolution is voxel volume

Answer 78

Pixel Phase Dimension x Pixel Frequency Dimension x Slice Thickness = Voxel Volume (mm^3)

Answer 79

- The amount of time it takes to fill k-space during data acquisition - Only affected by TR, NSA, Phase Matrix, Number of Slices (only in 3D), and ETL

Answer 80

TR x NSA x Phase Encodings

Answer 81

(TR x NSA x Phase Encodings) / ETL

Answer 82

TR x NSA x Phase Encodings x # of Slices

Answer 83

- T1 recovery - T2 decay - Proton density - Flow - Apparent diffusion coefficient - Perfusion - Diffusion

Answer 84

- TR - TE - Flip angle - TI - ETL - B value - FOV - Matrix

Answer 85

- The number of times that data is collected per TR period - Square root relationship with SNR - Directly proportional relationship with scan time

Answer 86

- Scan time doubled | - 41% increase in SNR

Answer 87

- Scan time quadrupled | - 100% increase in SNR

Answer 88

- Greatest impact on SNR | - Directly squared relationship with SNR

Answer 89

Signal quadrupled

Answer 90

Only 1/4 of signal is acquired

Answer 91

TR selected and SAR limitation

Answer 92

Slope of the slice select gradient and the transmitted bandwidth

Answer 93

Steep slice-select gradient slope and narrow transmit bandwidth

Answer 94

Shallow slice-select gradient and broad transmit bandwidth

Answer 95

- Number of times the echo is sampled per TR period during SE pulse sequence - Corresponds to the number of rephasing 180 degree RF pulse applied

Answer 96

Slice thickness selection

Answer 97

- Range of frequencies sampled during the time that the readout frequency gradient is active - Has a square root relation with SNR

Answer 98

40% of signal is lost

Answer 99

40% of signal gained

Answer 100

- An additional RF pulse with a 90 deg flip angle and wide transmission bandwidth (to saturate all tissues) strategically placed over areas of unwanted anatomy both inside or outside the FOV - Increase tissue heating

Answer 101

Either slice-select (axial) or frequency (coronal or sagittal) encoding gradients

Answer 102

- Applies and extra 90 deg RF pulse with a narrow transmission bandwidth (at the precessional frequency of fat, water, or sometimes silicone) before the application of the alpha pulse - Can be improved by applying a shim over the anatomy

Answer 103

Period of time bewteen the 90 deg saturation pulse and the alpha pulse

Answer 104

TR / Slice #

Answer 105

Period of time bewteeen the R phases (ventricular contraction) of the cardiac cycle

Answer 106

60,000 ms / BPM

Answer 107

Final 10% of the R to R interval

Answer 108

- Scan time decreases - Noise decreases - Aliasing increases

Answer 109

GE pulse sequence with specific TE values to better demonstrate areas where fat and water interface

Answer 110

- Uses a 90 deg alpha pulse and multiple 180 deg rephasing pulses per TR - Multiple lines of K-space filled per TR

Answer 111

- Increase motion - Increase blurring - Decrease SNR - Decrease magnetic susceptibility artifacts

Answer 112

- Combines FSE with a Partial Fourier technique to fill all lines of K-space during a single TR period - Reduces time but increases SAR (due to extra RF rephasing pulses used)

Answer 113

- Uses a reverse flip angle excitation pulse after the echo train to "drive" any residual transverse magnetization into the longitudinal plane so that it cannot be further excited at the beginning of the next TR cycle (causes T1 relaxation to occur quicker) - Yield hyperintense fluid signal compared to standard FSE

Answer 114

- Use an alpha pulse with a variable flip angle - Uses the frequency encoding gradient for rephasing - All GE images have some extent of T2* (cannot compensate for magnetic field inhomogeneities) - Sensitive to flow, extremely fast

Answer 115

- CGE - Steady State - FGE - Balanced Gradient Echo - Echo Planar Imaging

Answer 116

- Uses two excitation pulses with variable flip angles at TR time intervals less than the T1 and T2 times of the body's tissues in order to maintain RTM for the creation of stimulated echo (due to rephasing of the RTM by the second excitation pulse) - Maintain partial longitudinal and transverse magnetization at all times

Answer 117

The echo created by the application of the second excitation pulse if the steady state uses two 90 deg excitation pulses

Answer 118

- Incoherent Gradient Echo - Coherent Gradient Echo - Steady State Free Precession (SSFP)

Answer 119

- Only the gradient echo (FID) is sampled - Stimulated echo (RTM) is spoiled (dephased) - Typically used for T1 and sometimes PD

Answer 120

- Both the gradient echo (FID) and stimulated echo (RTM) are sampled - Rewinder gradient rephases RTM so it can contribute to image contrast - Typically used for T2*

Answer 121

- Only stimulated echo (RTM) is sampled - Rewinder gradient rephases RTM - Typically used for "truer" T2 weighted images (removes magnetic field inhomogeneities)

Answer 122

- Coherent or incoherent - Uses shorter TE by only transmitting part of an RF pulse and by only reading a portion of the echo (Partial Echo Technique) - Acquisition of an entire volume with a single breath hold - Temporal resolution enhancement during post contrast dynamic imaging

Answer 123

- Coherent - Uses a balanced gradient system (to correct phase errors in flowing blood and CSF) as well as larger flip angles - High SNR, good CNR, and very short scan times - Typically used to image the heart and great vessels, spinal column (esp c-spine), and iacs

Answer 124

- Uses blipped, or constant oscillation of the phase-encoding gradient in order to fill all lines of K-space during single TR period - K-space is filled linearly, line by line, in a stair-stepped fashion - Used for perfusion, spectroscopy - Problems include distortions and chemical shift artifacts - Fastest form of data acquisition

Answer 125

- Uses 90 deg excitation pulse, then 180 deg rephasing pulse, then a pulsing phase encoding gradient - Addition of the rephasing pulse helps to eliminate magnetic inhomogeneities and chemical shift - Longer than GE EPI but better image quality

Answer 126

- Uses a 90 deg excitation pulse, then a pulsing phase encoding gradient (no 180 deg rephasing pulse) - Shortest scan times but worse image quality than SE EPI

Answer 127

- Filled linearly from the center outwards - Shallow first in the center as contrast data - Steep next in the periphery as spatial resolution data - Typically used during FGE to compensate for poor SNR and CNR

Answer 128

- Filled starting in the center and spiraling outward using both the frequency and phase encoding gradients - Elliptical (demonstrates arterial flow and suppresses venous flow) - Propeller (used for motion suppression)

Answer 129

- Filled linearly with the outer lines being filled before contrast injection and inner lines filled after contrast injection - Dynamic angiography studies

Answer 130

- A mathematical formula that converts the frequency/time domain into the frequency/amplitude domain - Occurs directly after readout

Answer 131

-Occurs when areas with a very long T2 decay time remain bright on DWI trace images

Answer 132

Bright on DWI trace and dark on ADC maps

Answer 133

Dark on DWI trace and bright on ACD maps

Answer 134

As flow velocity increases, less flowing nuclei are present within the slice for both excitation and rephasing pulse, thus TOF effects increase

Answer 135

As flow velocity decreases, more flowing nuclei are present in the slice for excitation and rephasing pulse, thus TOF effects decrease

Answer 136

- Stationary spins always receive both the excitation and rephasing pulse, and flowing spins present within the slice for excitation have usually traveled out of the slice before being rephased (thus returning no signal - Only observable during SE sequences

Answer 137

- "Inflow effect" - How spins flowing perpendicular to a stack of slices enter the stack fresh (unsaturated) and produce more signal than stationary nuclei that receive repeated RF excitation (saturated)

Answer 138

-A type of MRA technique that uses an incoherent GE pulse sequence with GMN, as well as very specific imaging parameters

Answer 139

Provides larger FOV (lower resolution) and is suitable for imaging areas with slow flow (carotids)

Answer 140

Provides a smaller FOV (higher resolution) and is suitable for imaging areas of fast flow (COW)

Answer 141

- Flip angle: 45-60 deg - Short TR: 20-50 ms - TE: minimum

Answer 142

-A type of MRA technique that uses a GE pulse sequence with a small flip angle to saturate the signal from stationary tissue, as well as to two additional bi-polar gradient pulses (VENC) to create phase changes in flowing blood

Answer 143

- Fast flowing bloods such as within arteries with small circumferences - COW, vertebral arteries

Answer 144

- Slow flowing blood, such as within arteries with a large circumference - Aorta, femoral

Answer 145

- Diffusion gradients applied along all three axes independently to show directional differences - Display white matter

Answer 146

- Diffusion gradients applied along all three axes simultaneously to show non-directional differences - Display gray matter

Answer 147

- Parameter that controls the duration, strength, and amplitude of the gradient pulses on either side of the 180 deg RF pulse used in DWI and DTI - 500-1500 s/mm - Higher the B value, more DW is present

Answer 148

The movement of molecules within extra-cellular spaces due to random thermal motion

Answer 149

Net displacement of molecules within the extracellular space due to diffusion

Answer 150

- Allows the differences between tagged and untagged spins - Images are usually acquired before, during, and after gad injection - Measures quality of vascular supply to tissues - Information are displayed on a Time Intensity Curve and Cerebral Blood Volume Map (CBV)

Answer 151

Volume of blood that flows into one gram of tissue (a measure of the regional blood flow in tissues)

Answer 152

- Signal decay curve that is obtained after all data is acquired - Used to determine blood volume, transient time, and the measurement of perfusion

Answer 153

- Map obtained by the combination of multiple time-intensity curves for images acquired during and after contrast injection - Provided information on the overall blood volume delivered to the cerebrum

Answer 154

- High temporal resolution | - Permit dynamic imaging of an enhancing lesion

Answer 155

Sylvian fissure

Answer 156

Basilar artery

Answer 157

VII and VIII

MRI All-In-One Flashcards

(188 cards)